Magnetic actuator

Abstract

A magnetic actuator includes a first yoke, an armature which is provided inside the first yoke and made movable in reciprocating motion along a first direction inside the first yoke, first and second coils fitted inside the first yoke, a pair of second yokes affixed to the first yoke along a second direction, and permanent magnets affixed to the second yokes in a manner that the permanent magnets are positioned face to face with the armature. In the magnetic actuator thus constructed, fluxes generated by the first and second coils pass through first magnetic circuits whereas fluxes generated by the permanent magnets pass through second magnetic circuits differing from the first magnetic circuits.

1. A magnetic actuator comprising:
 a first yoke including an assembly of laminated metal sheets; 
 a second yoke affixed to the first yoke, wherein the first yoke has a first surface perpendicular to a lamination direction of the metal sheets and the second yoke is attached to the first surface of the first yoke; 
 a permanent magnet; 
 an armature located inside the first yoke and movable in reciprocating motion over a stroke between a first position and a second position, along a first direction; and 
 at least one coil, wherein
 a flux generated by the at least one coil passes through a first magnetic circuit including the armature and the first yoke to move the armature toward one of the first and second positions, and 
 a flux generated by the permanent magnet passes through a second magnetic circuit including the permanent magnet, the first yoke, the second yoke, and the armature to hold the armature at one of the first and second positions. 
 
 
     
     
       2. The magnetic actuator according to  claim 1 , wherein the permanent magnet is located between the first yoke and the second yoke, at an end surface of the second yoke facing the armature. 
     
     
       3. The magnetic actuator according to  claim 1 , including
 a second magnetic air gap between the second position and an end surface of the armature facing the second position when the armature is held at the first position, and 
 a first magnetic air gap, differing from the second magnetic air gap, between the first position and an end surface of the armature facing the first position when the armature is held at the second position. 
 
     
     
       4. The magnetic actuator according to  claim 1 , wherein the second yoke is oriented along the first direction. 
     
     
       5. A magnetic actuator comprising:
 a first yoke including an assembly of laminated metal sheets; 
 a second yoke affixed to the first yoke; 
 a permanent magnet; 
 an armature located inside the first yoke and movable in reciprocating motion over a stroke between a first position and a second position, along a first direction, wherein the second yoke is oriented along a second direction which is perpendicular to the first direction; and 
 at least one coil, wherein
 a flux generated by the at least one coil passes through a first magnetic circuit including the armature and the first yoke to move the armature toward one of the first and second positions, and 
 a flux generated by the permanent magnet passes through a second magnetic circuit including the permanent magnet, the first yoke, the second yoke, and the armature to hold the armature at one of the first and second positions. 
 
 
     
     
       6. The magnetic actuator according to  claim 1 , wherein the second yoke includes an assembly of laminated metal sheets. 
     
     
       7. The magnetic actuator according to  claim 1 , wherein a first yoke section of the first yoke at the second position of the armature has a smaller cross-sectional area than a second yoke section of the first yoke at the first position of the armature. 
     
     
       8. The magnetic actuator according to  claim 1 , wherein the first yoke has stepped surfaces creating a partial air gap between the first yoke and the armature when the armature is held at either of the first and second positions. 
     
     
       9. The magnetic actuator according to  claim 1  further comprising a jack bolt fitted to the second yoke, wherein the permanent magnet is affixed to the second yoke and an air gap between the armature and the permanent magnet can be varied by operating the jack bolt, so a metal sheet can be inserted between the second yoke and the first yoke. 
     
     
       10. The magnetic actuator according to  claim 1 , wherein the at least one coil includes multiple coils. 
     
     
       11. The magnetic actuator according to  claim 1 , wherein an end portion of the armature through which the fluxes pass, facing the first yoke, has a smaller cross-sectional area than other portions of the armature through which the fluxes pass. 
     
     
       12. The magnetic actuator according to  claim 1 , wherein the armature includes an assembly of laminated metal sheets. 
     
     
       13. The magnetic actuator according to  claim 12 , wherein the laminated metal sheets are bound together with solid end plates at both ends of the assembly of the laminated metal sheets. 
     
     
       14. The magnetic actuator according to  claim 13 , wherein peripheral surfaces of each of the end plates are positioned inside of end surfaces of the assembly of laminated metal sheets. 
     
     
       15. The magnetic actuator according to  claim 1 , wherein the permanent magnet is located within the first yoke and the second yoke, and between elements of the second yoke. 
     
     
       16. The magnetic actuator according to  claim 1 , further comprising an actuating mechanism moving the armature along the first direction. 
     
     
       17. The magnetic actuator according to  claim 1 , including a first coil and a second coil fitted to the first yoke. 
     
     
       18. The magnetic actuator according to  claim 1 , wherein the permanent magnet is located in the second magnetic circuit, which is distinct from the first magnetic circuit. 
     
     
       19. A magnetic actuator comprising:
 an armature located inside the first yoke and movable in reciprocating motion over a stroke between a first position and a second position, along a first direction; 
 a coil surrounding the armature; 
 a first yoke including an assembly of laminated metal sheets and having an end face facing a side face of the armature, the first yoke including a holding part for holding the armature and an extending part extending from the end face to the holding part along an outer circumference of the coil; 
 a permanent magnet; and 
 a second yoke including a mounting part attached to the first yoke and a connecting part connected to the permanent magnet, wherein 
 the first yoke has a first surface perpendicular to a lamination direction of the metal sheets, and 
 the second yoke is attached to the first surface of the first yoke. 
 
     
     
       20. The magnetic actuator according to  claim 17 , wherein a magnetomotive force produced by the first coil differs from a magnetomotive force produced by the second coil.